This invention relates to techniques of storing and rendering streaming multimedia content at different speeds, and for correlating timelines of media streams that have been timeline-altered by varying techniques and degrees.
Multimedia streaming-the continuous delivery of synchronized media data like video, audio, text, and animation-is a critical link in the digital multimedia revolution. Today, streamed media is primarily about video and audio, but a richer, broader digital media era is emerging with a profound and growing impact on the Internet and digital broadcasting.
Synchronized media means multiple media objects that share a common timeline. Video and audio are examples of synchronized mediaxe2x80x94each is a separate data stream with its own data structure, but the two data streams are played back in synchronization with each other. Virtually any media type can have a timeline. For example, an image object can change like an animated .gif file: text can change and move, and animation and digital effects happen over time. This concept of synchronizing multiple media types is gaining greater meaning and currency with the emergence of more sophisticated media composition frameworks implied by MPEG-4, Dynamic HTML, and other media playback environments. The term xe2x80x9cstreamingxe2x80x9d is used to indicate that the data representing the various media types is provided over a network to a client computer on a realtime, as-needed basis, rather than being pre-delivered in its entirety before playback. Thus, the client computer renders streaming data as it is received from a network server, rather than waiting for an entire xe2x80x9cfilexe2x80x9d to be delivered.
The widespread availability of streaming multimedia enables a variety of informational content that was not previously available over the Internet or other computer networks. Live content is one significant example of such content. Using streaming multimedia, audio, video, or audio/visual coverage of noteworthy events can be broadcast over the Internet as the events unfold. Similarly, television and radio stations can transmit their live content over the Internet.
A U.S. Patent Application entitled xe2x80x9cMultimedia Timeline Modification in Networked Client/Server Systems,xe2x80x9d filed Sep. 15, 1998, Ser. No. 09/153,664, by inventors Anoop Gupta and Nosa D. Omoigui, describes a system that allows a user to vary the playback speed of streaming multimedia content using time-scale modification technology. It was noted that both linear and non-linear timeline alteration techniques might be used.
When using linear techniques, time modification is applied consistently in times and across all individual streams of a composite media stream. With non-linear techniques, on the other hand, some segments of an individual or composite stream might be more highly expanded or compressed (in time) than other segments. This presents problems in switching and synchronizing between different versions of streams that have been non-linearly altered by different amounts or through the use of different non-linear techniques. These problems are addressed by the invention.
The invention utilizes time-scale modification so that a user can vary the speed of streaming content without destroying its intelligibility. In accordance with the invention, a user selects multimedia content from a menu presented at a network client computer. In addition, the user selects a playback speed, indicating the speed at which the multimedia should be rendered relative to its default speed. In the case of non-linearly altered streams, the user selects from available levels of alteration, such as xe2x80x9cnormal,xe2x80x9d xe2x80x9cpauses removed,xe2x80x9d and xe2x80x9csummaryxe2x80x9d levels of non-linear time compression.
Multiple versions of the requested multimedia content are stored at a server. In response to the selected playback speed or selected level of non-linear compression, the appropriate version is streamed to the client computer.
In addition to storing multiple versions of the multimedia content, the server maintains data structures that indicate timeline correlations between the various stored versions. The client refers to these stored timeline correlations when changing between the versions in response to client requests, so that playback can be started anew with a new stream at the point in the content where the change was requested by the client.
In the embodiment described herein, one version of the multimedia stream is considered to be a primary or reference version. This is usually the version having an unaltered timeline, corresponding to a 1.0 speed factor. Associated with this primary media stream is a table or other data object that is indexed by the presentation times of the primary media stream. For each presentation time of the primary media stream, the table indicates the timeline-correlated presentation times of the other, timeline-altered, media streams.
In addition, further data objects or elements are provided in conjunction with the timeline-altered media streams. These data objects are indexed by the presentation times of the timeline-altered media stream, and map such presentation times to the time-correlated presentation times of the primary media stream. One way to index these data objects is to associate and send them with the actual data units of the time-altered media streams.
When switching playback from a first time-altered media stream to a second time-altered media stream, the client stops the first media stream and notes the presentation time (in the first media stream) at which playback was stopped. The client then refers to the table associated with the first media stream and from it determines the timeline-correlated presentation time in the primary media stream. With that information, the client refers to the table associated with the primary media stream, and determines the time-correlated presentation time in the second media stream. The client then initiates playback of the second media stream at or before this time-correlated presentation time.